“I want to add my voice in support of Muslims in our community and around the world,” Mr. Zuckerberg wrote inFacebook post on Wednesday night, in which he again invoked his newborn child. “After theParis attacks and hate this week, I can only imagine the fear Muslims feel that they will be persecuted for the actions of others.

“As a Jew,” he wrote, “my parents taught me that we must stand up against attacks on all communities. Even if an attack isn’t against you today, in time attacks on freedom for anyone will hurt everyone.

“If you’re a Muslim in this community, as the leader of Facebook I want you to know that you are always welcome here and that we will fight to protect your rights and create a peaceful and safe environment for you.”

The message came amid rising anti-Muslim commentary in the wake of the attack in California anda backlash against comments by Donald J. Trump, the leading Republican candidate for president. Mr. Zuckerberg did not single out Mr. Trump or anyone else.

But he has shown a new level of openness since July, whenhe announced that he and Dr. Chan were expecting a baby.

As of Thursday afternoon, his post had been shared more than 184,000 times, and had been liked nearly 1.3 million times. It also became a forum on bias and race, with more than 58,000 comments.

Some expressed appreciation for his support of Muslims and his denouncements of stereotypes that arise after episodes of extremist Islamist violence.